Role of Strain-Specific Reproductive Patterns in the Appearance of Mammary Tumors in Atrazine-Treated Rats

Atrazine has been a major agricultural herbicide in the U.S. for more than 25 years. It is used for the control of broadleaf and grass weeds in corn and sorghum crops. Because of its common use, the toxicity of atrazine has been the subject of many studies. Atrazine is not toxic with acute administration, with an oral and dermal LD 50 of greater than 3,000 mg/kg. In tests of mutagenicity, atrazine have been negative in more than 50 tests ( 1 ). Atrazine is not a teratogen or a reproductive toxin, and lacks carcinogenic activity in male and female mice and Fischer 344 (F-344) rats, as well as in male Sprague-Dawley (SD) rats. Five tests of the tumorogenicity of atrazine in SD rats have been conducted since the 1960s. Two of these tests, which assessed atrazine at doses up to 500 ppm, produced negative results, while 3 other studies have shown an earlier